I was interrupted and posted before completing my last post, so a disclaimer. I never actually traded these ideas, it was more in a formulation stage. I was having some of the same issues with backtesting that you were having, with trying to compare relative strength on past market days. I downloaded several months of intraday data for a limited number of symbols from esignal that I used for some very limited backtesting, and was in the process of paper trading.
This strategy was so counter to what I was doing at the time in my day trading that I had some difficulty trying to retrain myself to avoid the counter-trend trading. That is one reason that I tried to incorporate using pullbacks, so that I could stick with buying dips and selling rallies. The difference is that you are buying dips in stronger stocks on up market days and selling rallies in weaker stocks on weak market days, as opposed to picking a top for the strongest stock on your screen because "it can't go any higher".
FYI, sometimes the "pullback" for a really strong stock might not happen. You might see a couple of hours during the day where it plateaus and just goes sideways. When that happens, especially if the rest of the market has pulled back any your stock won't budge, that might be just as good or better than an actual reduction in price. If and when the market resumes rally, that stock has a pretty good chance to take off as well.
This strategy was so counter to what I was doing at the time in my day trading that I had some difficulty trying to retrain myself to avoid the counter-trend trading. That is one reason that I tried to incorporate using pullbacks, so that I could stick with buying dips and selling rallies. The difference is that you are buying dips in stronger stocks on up market days and selling rallies in weaker stocks on weak market days, as opposed to picking a top for the strongest stock on your screen because "it can't go any higher".
FYI, sometimes the "pullback" for a really strong stock might not happen. You might see a couple of hours during the day where it plateaus and just goes sideways. When that happens, especially if the rest of the market has pulled back any your stock won't budge, that might be just as good or better than an actual reduction in price. If and when the market resumes rally, that stock has a pretty good chance to take off as well.